It's the second year with Paris-Nice testing this experiment. Last year they did the same, although it was a flat TT. I think it doesn't make much of a difference except for the fact that the team GC leader can go solo on the last climb to try and gain a few more seconds, but for the most part any team need several cyclists, otherwise the speed is going to be slower. A good example this year was BORA, which left only three riders after the first climb, and clearly that wasn't enough and led them into losing time.
To be honest, for flat TTTs, I prefer the traditional rules where it's the 3rd-4th-5th cyclist the one that marks the time for the whole team. It is more 'team-like'. If there is a final climb, I can see the benefit of these rules.